1 .. SPDX-License-Identifier: GPL-2.0 2 3 ============== 4 Nitro Enclaves 5 ============== 6 7 Overview 8 ======== 9 10 Nitro Enclaves (NE) is a new Amazon Elastic Compute Cloud (EC2) capability 11 that allows customers to carve out isolated compute environments within EC2 12 instances [1]. 13 14 For example, an application that processes sensitive data and runs in a VM, 15 can be separated from other applications running in the same VM. This 16 application then runs in a separate VM than the primary VM, namely an enclave. 17 It runs alongside the VM that spawned it. This setup matches low latency 18 applications needs. 19 20 The current supported architectures for the NE kernel driver, available in the 21 upstream Linux kernel, are x86 and ARM64. 22 23 The resources that are allocated for the enclave, such as memory and CPUs, are 24 carved out of the primary VM. Each enclave is mapped to a process running in the 25 primary VM, that communicates with the NE kernel driver via an ioctl interface. 26 27 In this sense, there are two components: 28 29 1. An enclave abstraction process - a user space process running in the primary 30 VM guest that uses the provided ioctl interface of the NE driver to spawn an 31 enclave VM (that's 2 below). 32 33 There is a NE emulated PCI device exposed to the primary VM. The driver for this 34 new PCI device is included in the NE driver. 35 36 The ioctl logic is mapped to PCI device commands e.g. the NE_START_ENCLAVE ioctl 37 maps to an enclave start PCI command. The PCI device commands are then 38 translated into actions taken on the hypervisor side; that's the Nitro 39 hypervisor running on the host where the primary VM is running. The Nitro 40 hypervisor is based on core KVM technology. 41 42 2. The enclave itself - a VM running on the same host as the primary VM that 43 spawned it. Memory and CPUs are carved out of the primary VM and are dedicated 44 for the enclave VM. An enclave does not have persistent storage attached. 45 46 The memory regions carved out of the primary VM and given to an enclave need to 47 be aligned 2 MiB / 1 GiB physically contiguous memory regions (or multiple of 48 this size e.g. 8 MiB). The memory can be allocated e.g. by using hugetlbfs from 49 user space [2][3][7]. The memory size for an enclave needs to be at least 50 64 MiB. The enclave memory and CPUs need to be from the same NUMA node. 51 52 An enclave runs on dedicated cores. CPU 0 and its CPU siblings need to remain 53 available for the primary VM. A CPU pool has to be set for NE purposes by an 54 user with admin capability. See the cpu list section from the kernel 55 documentation [4] for how a CPU pool format looks. 56 57 An enclave communicates with the primary VM via a local communication channel, 58 using virtio-vsock [5]. The primary VM has virtio-pci vsock emulated device, 59 while the enclave VM has a virtio-mmio vsock emulated device. The vsock device 60 uses eventfd for signaling. The enclave VM sees the usual interfaces - local 61 APIC and IOAPIC - to get interrupts from virtio-vsock device. The virtio-mmio 62 device is placed in memory below the typical 4 GiB. 63 64 The application that runs in the enclave needs to be packaged in an enclave 65 image together with the OS ( e.g. kernel, ramdisk, init ) that will run in the 66 enclave VM. The enclave VM has its own kernel and follows the standard Linux 67 boot protocol [6][8]. 68 69 The kernel bzImage, the kernel command line, the ramdisk(s) are part of the 70 Enclave Image Format (EIF); plus an EIF header including metadata such as magic 71 number, eif version, image size and CRC. 72 73 Hash values are computed for the entire enclave image (EIF), the kernel and 74 ramdisk(s). That's used, for example, to check that the enclave image that is 75 loaded in the enclave VM is the one that was intended to be run. 76 77 These crypto measurements are included in a signed attestation document 78 generated by the Nitro Hypervisor and further used to prove the identity of the 79 enclave; KMS is an example of service that NE is integrated with and that checks 80 the attestation doc. 81 82 The enclave image (EIF) is loaded in the enclave memory at offset 8 MiB. The 83 init process in the enclave connects to the vsock CID of the primary VM and a 84 predefined port - 9000 - to send a heartbeat value - 0xb7. This mechanism is 85 used to check in the primary VM that the enclave has booted. The CID of the 86 primary VM is 3. 87 88 If the enclave VM crashes or gracefully exits, an interrupt event is received by 89 the NE driver. This event is sent further to the user space enclave process 90 running in the primary VM via a poll notification mechanism. Then the user space 91 enclave process can exit. 92 93 [1] https://aws.amazon.com/ec2/nitro/nitro-enclaves/ 94 [2] https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html 95 [3] https://lwn.net/Articles/807108/ 96 [4] https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html 97 [5] https://man7.org/linux/man-pages/man7/vsock.7.html 98 [6] https://www.kernel.org/doc/html/latest/x86/boot.html 99 [7] https://www.kernel.org/doc/html/latest/arm64/hugetlbpage.html 100 [8] https://www.kernel.org/doc/html/latest/arm64/booting.html
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